When a structure or structural system is excited, elements of the structure may get displaced relative to one another. If such displacements are large, or if they occur periodically, they may have serious impact on the conditions of the structure, and may cause severe damages or even result in a collapse.
Dampers play an important role in the protection of structures such as buildings, and they exist in numerous variants. Dampers are typically damping the motion by means of a friction force between two parts attached to the frame structure of the building, or by means of a fluid being pressed to flow between two chambers through a restriction. Other similar well-known methods of damping motion or vibrations exist. Some dampers are actively changing the damping effect corresponding to external conditions, and other dampers are passive dampers having a constant damping characteristic. The active dampers are expensive and technically complicated devices, which need extensive maintenance in order to work when needed. Further, they are prone to malfunctions, e.g. leaking of hydraulic fluids or breakdown of electronic control systems.
WO 2011038742 discloses a passive damper that is constructed with overlapping sets of plates connected by a bolt with damping pads arranged between the plates and the bolts applying a compression force on the plates and the damping pads therebetween. The damper impedance can be adjusted by changing the compression force. However, this can only be done during installation or during service, and not in response to an event such as a seismic event.
Passive dampers with a variable damping characteristics are sometimes desirable but no commercially viable dampers of such kind are presently available.